1. Field of the Invention
The present invention relates to a hydrogen peroxide removal equipment for treating a waste water containing hydrogen peroxide. The present invention also relates to a hydrogen peroxide removal equipment capable of treating a waste gas containing an organic substance together with the waste water containing hydrogen peroxide.
2. Description of the Prior Art
When hydrogen peroxide is contained in the waste water, COD (Chemical Oxygen Demand) increases. Therefore, it is required to surely remove the hydrogen peroxide in the waste water. Furthermore, when the hydrogen peroxide is untreated in a waste water treating process of a fluorine containing waste water, minute bubbles of oxygen generated from the hydrogen peroxide adhere to a flock of sedimentation in a coagulation-sedimentation process to hinder the sedimentation itself, consequently degrading the treated water. Therefore, in the waste water treating process, the hydrogen peroxide containing waste water is treated separately from the general coagulation-sedimentation process.
Conventionally, as a hydrogen peroxide removal equipment for removing the hydrogen peroxide in the waste water, an equipment as shown in FIG. 5 has been known (Japanese Patent Laid-Open Publication No. HEI 6-91258). This hydrogen peroxide removal equipment 70 has in its treatment tank 33 a contact section 111 which is defined by a wire gauze 105 and a peripheral wall 106 and is opening upwardly and a sedimentation section 112 which surrounds the contact section 111 via the peripheral wall 106. Downwardly around the contact section 111 are provided an opening 116 for making the sedimentation section 112 communicate with the contact section 111 and a supply port 104 for letting the waste water horizontally flow into the contact section 111. In operation, a granular activated carbon is preparatorily put into the contact section 111 at a rate of 1 to 35% of the effective tank capacity. In this state, the hydrogen peroxide containing waste water is introduced from a pipe 7A into the treatment tank 33 through a supply port 103 provided at the bottom of the tank. This hydrogen peroxide containing waste water flows into the contact section 111 through the wire gauze 105 to fill the contact section 111 therewith. On the other hand, the hydrogen peroxide containing waste water (of which flow rate is adjusted by a valve 120) is introduced into the contact section 111 from a branched pipe 7B through the horizontal supply port 104. As a result, an eddying current is generated together with an ascending current inside the contact section 111, and the granular activated carbon and the hydrogen peroxide containing waste water are put in contact with each other, so that the hydrogen peroxide is decomposed into water and oxygen by a catalyzing effect of the activated carbon. The waste water obtained through the treatment process overflows from the contact section 111 to come into the sedimentation section 112, and then it is discharged from an outlet port 118 provided behind a baffle plate 117 through a pipe 21. In the present case, even when the granular activated carbon overflows together with the treated waste water to the sedimentation section 112, the granular activated carbon stays in the sedimentation section 112 for a time to settle there and then returns to the contact section 111 through the opening 106. Therefore, only a supernatant water is discharged from the outlet port 118 of the sedimentation section 112.
This type of hydrogen peroxide removal equipment is, as exemplarily shown in FIG. 4, often incorporated into a waste water treatment system 80 for treating the hydrogen peroxide containing waste water generated in a semiconductor plant 1. Generally, a production room 100 of the semiconductor plant 1 for producing ICs (Integrated Circuits) and the like is provided with a number of production equipments such as an equipment 37 for executing so-called the RCA cleaning process (a cleaning method developed by RCA Corp., typically consisting of a first stage for removing each organic substance by means of NH.sub.4 OH, HCl and H.sub.2 O and a second stage for removing alkaline metals and heavy metals by means of HCl, H.sub.2 O.sub.2 and H.sub.2 O) and an equipment 2 using organic solvents such as acetone and isopropyl alcohol. The hydrogen peroxide containing waste water from the RCA cleaning equipment 37 and so forth flows into a raw water tank 5 through a pipe 26, and the quantity and quality of the water are adjusted to a certain degree in the raw water tank 5. Subsequently, the waste water is introduced into a hydrogen peroxide removal equipment 70 through a pipe 7 by a raw water tank pump 6. In the tank 33 of the hydrogen peroxide removal equipment 70, the hydrogen peroxide in the waste water is decomposed into oxygen and water as described hereinbefore. Then, the waste water obtained through the treatment process flows into a treated water tank 23 through the pipe 21. The quality of the water in the treated water tank 23 is inspected by an oxidation reduction electrometer 34.
Further, as shown in FIG. 4, a waste gas containing any organic substance (organic substance containing waste gas) from the RCA cleaning equipment 37, the organic solvent using equipment 2 and so forth is treated by a treatment system 90 for the organic substance containing waste gas separately from the waste water treatment system 80 for the hydrogen peroxide containing waste water. That is, the organic substance containing waste gas 27 is generated from the organic solvent using equipment 2, the RCA cleaning equipment 37 and so forth of the production room 100, discharged by a production room exhaust fan 35 provided outside the production room 100, and then introduced via an exhaust duct 36A into activated carbon adsorption towers 32A and 32B. Then, each organic substance contained in the waste gas is adsorbed on the activated carbon stuffed in the activated carbon adsorption towers 32A and 32B, so that each organic substance is removed from the waste gas. It is to be noted that the organic substance adsorption process is not intended to decompose each organic substance, and therefore, when the amount of each organic substance that is adsorbed on the activated carbon reaches an adsorption saturation amount, it is required to desorb each organic substance from the activated carbon. Therefore, normally two or more activated carbon adsorption towers are provided, and by repeating the adsorption and desorption alternately in the activated carbon adsorption towers 32A and 32B, the organic substance containing waste gas is continuously treated as a whole. Each desorbed organic substance is collected through an exhaust duct 36B or further treated in a waste water treating equipment.
The quantity and quality of the hydrogen peroxide containing waste water generated in the semiconductor plant 1 vary greatly depending on the day and time. This is because the semiconductor plant 1 has a number of production equipments such as the RCA cleaning equipment 37 and the organic solvent using equipment 2, and on the convenience of the production process, chemicals or the like containing hydrogen peroxide are used irregularly in time. Furthermore, when sterilizing and cleaning the production equipments with hydrogen peroxide, a great amount of hydrogen peroxide containing waste water is generated. Therefore, if the quantity and quality of the hydrogen peroxide containing waste water are adjusted to a certain extent in the raw water tank 5, the waste water flowing into the hydrogen peroxide removal equipment 70 greatly increases in amount, and the resulting hydrogen peroxide concentration sometimes greatly increases.
However, the hydrogen peroxide removal equipment 70 has such a problem that it can hardly cope with the increase in amount of the hydrogen peroxide containing waste water and the increase of the hydrogen peroxide concentration. The reason of the above is as follows. That is, a specified amount of granular activated carbon is merely made to circulate with the eddying current in the same direction as that of the waste water, and therefore, the granular activated carbon cannot be uniformly distributed throughout the entire inner region of a tank 111. Furthermore, since there is a small variation of the contact surfaces of the granular activated carbon and the waste water, there is a low capacity for removing the hydrogen peroxide.
Generally speaking, there is an operational technique to limit the amount of inflow water when the quality of the inflow waste water is worsened (when the hydrogen peroxide concentration is increased in this case) in the waste water treating equipment. However, when the amount of inflow water is limited in the prior art hydrogen peroxide removal equipment 70, a reduced stirring force results inside the tank 111 to cause sedimentation of the activated carbon on the bottom of the tank, and this reduces the function of the activated carbon as a catalyst. Furthermore, the semiconductor plant originally has the tendency that the increase in amount of the hydrogen peroxide containing waste water and the increase of the hydrogen peroxide concentration occur concurrently, and therefore, such an operational technique can hardly cope with the above matter in many cases.